Particle beam assisted modification of thin film materials

ABSTRACT

Several examples of a method for processing a substrate are disclosed. In a particular embodiment, the method may include: disposing a substrate having an upper surface and a lower surface on a platen contained in a chamber; generating a plasma containing a plurality of charged particles above the upper surface of the substrate, the plasma having a cross sectional area equal to or greater than a surface area of the upper surface of the substrate; applying a first bias voltage to the substrate to attract the charged particles toward the upper surface of the substrate; introducing the charged particles to a region extending under entire upper surface of the substrate; and initiating, concurrently, a first phase transformation in the region from the amorphous phase to a crystalline phase.

PRIORITY

This application claims priority to a Provisional Application No.60/987629 titled “Particle Beam Assisted Modification of Thin FilmMaterials” and filed on Nov. 13, 2007; a Provisional Application No.:60/987667 titled “Particle Beam Assisted Modification of Thin FilmMaterials” and filed on Nov. 13, 2007; and a Provisional Application60/987,650 titled “Particle Beam Assisted Modification of Thin FilmMaterials” and filed on Nov. 13, 2007, each of which is incorporated inentirety by reference.

RELATED APPLICATIONS

This application is related to co-pending application Ser. No. ______titled “Particle Beam Assisted Modification of Thin Film Materials” andfiled on ______, and co-pending application Ser. No. ______ titled“Particle Beam Assisted Modification of Thin Film Materials” and filedon ______. Each of the co-pending applications are incorporated inentirety by reference.

FIELD

This disclosure relates to a system and technique for processing asubstrate, more particularly, to a system and technique for forming asubstrate crystalline phase.

BACKGROUND

The widespread adoption of emerging technologies such as flat paneldisplays (FPD) and solar cells depends on the ability to manufactureelectrical devices on low cost substrates. In manufacturing FPD, pixelsof a typical low cost flat panel display (FPD), are switched by thinfilm transistors (TFT) which may be typically manufactured on thin (−50nm thick) films of amorphous silicon deposited on inert, glasssubstrates. However, improved FPDs demand better performing pixel TFTs,and it may be advantageous to manufacture high performance controlelectronics directly onto the panel. One advantage may be to eliminatethe need for costly and potentially unreliable connections between thepanel and external control circuitry.

Current FPDs contain a layer of Si that is deposited onto the glasspanel of the display via a low temperature deposition process such assputtering, evaporation, plasma enhanced chemical vapor deposition(PECVD), or low pressure chemical vapor deposition (LPCVD) process. Suchlow temperature processes are desirable, as the panel used tomanufacture FPD tends to be amorphous and has glass transitiontemperature of approximately 600° C. If manufactured above 600° C., thepanel may have a non-uniform or uneven structure or surface. Highertemperature tolerant glass panels such as quartz or sapphire panelexist; however, the high cost of such glasses discourages their use.Further cost reduction would be possible if cheaper, lower temperaturetolerant glass or plastic panels could be used.

The low temperature deposition process, however, does not yield optimalSi film. As known in the art, solid Si has three common phases:amorphous, poly-crystalline, and mono-crystalline phases. If Si isdeposited at low temperature, the deposited Si film tends to be in anamorphous phase. The channels of thin film transistors based onamorphous Si film may have lower mobility compared to those on eitherpoly-crystalline Si or mono-crystalline Si films.

To obtain a polycrystalline or mono-crystalline Si layer, the panel mayundergo further processes to convert the amorphous Si film to eitherpolycrystalline or mono-crystalline film. To obtain a panel withpoly-crystalline Si film, the panel may undergo an excimer laserannealing (ELA) process. An example of the ELA process may be found inmore detail in U.S. Pat. No. 5,766,989. To obtain a panel with largercrystals, the panel may undergo a process known as Sequential LateralSolidification (“SLS”) process. An example of SLS process may be foundin U.S. Pat. No. 6,322,625. Although ELA and SLS processes may result ina panel with mono-crystalline or poly-crystalline Si thin film, eachprocess is not without disadvantages. For example, excimer lasers usedin both processes may be expensive to operate, resulting in an expensiveTFT. In addition, the duty cycle may not be optimum for the bestconversion of amorphous Si into crystalline Si. Further, the excimerlaser may have pulse-to-pulse variations and spatial non-uniformity inthe delivered power which may affect the uniformity of the processes.There may also be intra-pulse non-uniformity which may be caused by forexample, self-interference of the beam. Such inter-pulse and intra-pulsenon-uniformity may result in Si films with non-uniform crystals.

As such, new methods and apparatus for particle processing for the costeffective and production worthy manufacture of high quality crystallinematerials on low temperature substrates are needed.

SUMMARY

Several examples of a method for processing a substrate are disclosed.In a particular embodiment, the method may include: disposing asubstrate having an upper surface and a lower surface on a platencontained in a chamber; generating a plasma containing a plurality ofcharged particles above the upper surface of the substrate, the plasmahaving a cross sectional area equal to or greater than a surface area ofthe upper surface of the substrate; applying a first bias voltage to thesubstrate to attract the charged particles toward the upper surface ofthe substrate; introducing the charged particles to a region extendingunder entire upper surface of the substrate; and initiating,concurrently, a first phase transformation in the region from theamorphous phase to a crystalline phase.

The present disclosure will now be described in more detail withreference to exemplary embodiments thereof as shown in the accompanyingdrawings. While the present disclosure is described below with referenceto exemplary embodiments, it should be understood that the presentdisclosure is not limited thereto. Those of ordinary skill in the arthaving access to the teachings herein will recognize additionalimplementations, modifications, and embodiments, as well as other fieldsof use, which are within the scope of the present disclosure asdescribed herein, and with respect to which the present disclosure maybe of significant utility.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to facilitate a fuller understanding of the present disclosure,reference is now made to the accompanying drawings, in which likefeatures are referenced with like numerals. These figures should not beconstrued as limiting the present disclosure, but are intended to beexemplary only.

FIG. 1 is a block diagram of various mechanisms through which amorphousmaterial may transform into crystalline material.

FIG. 2 shows a graph of the depth of Ar ions introduced to a Sisubstrate according to one embodiment of the present disclosure.

FIG. 3 shows block diagram of a system for processing a substrateaccording to one embodiment of the present disclosure.

FIG. 4 shows a block diagram of a particular exemplary system of thesystem shown in FIG. 3.

FIG. 5 shows a block diagram of another system for processing asubstrate according to another embodiment of the present disclosure.

FIG. 6 shows a graph comparing the temperature of a substrate irradiatedwith a laser beam or a particle beam.

FIG. 7 shows a graph of the temperature of a substrate irradiated with afocused particle beams according to another embodiment of the presentdisclosure.

FIG. 8A-8B show a method that can be incorporated into manufacturing ofa solar cell according to another embodiment of the present disclosure.

FIG. 9A-9C show another method that can be incorporated intomanufacturing of a solar cell according to another embodiment of thepresent disclosure.

FIG. 10A-10D show another method that can be incorporated intomanufacturing of a solar cell according to another embodiment of thepresent disclosure.

DETAILED DESCRIPTION

To overcome the above-identified and other deficiencies of existinglaser-based thin film materials processing, several embodiments ofparticle based processing are disclosed. The particle-based processingmay be advantageous as it may promote non-equilibrium processes. Inaddition, particle parameters may be controlled with much more precisionthan parameters of the laser. Examples of the particle parameters mayinclude spatial parameters (such as beam size and current densities),particle flux (and/or beam current), particles species, and particledose etc. . . .

In the present disclosure, several embodiments are disclosed in contextto a beamline ion implantation system and a plasma based substrateprocessing system such as, for example, a plasma assisted doping (PLAD)system or plasma immersion ion implantation (PIII) system. However,those of ordinary skill in the art should recognize that the presentdisclosure may be equally applicable to other systems including othertypes of particle based system. The term “particles” used herein mayrefer to sub-atomic, atomic, or molecular particles, charged or neutral.For example, the particles may be protons; ions, atomic or molecular; orgas clusters.

In the present disclosure, several embodiments are described in contextto a substrate. The substrate may be a wafer (e.g. Si wafer) or asubstrate comprising a plurality of films. In addition, the substratemay be an elemental substrate containing only one element (e.g. Si waferor metal foil); a compound substrate containing more than one element(e.g. SiGe, SiC, InTe, GaAs, InP, GaInAs, GaInP; CdTe; CdS; andcombinations of (Cu, Ag and/or Au) with (Al, Ga, and/or In) and (S, Seand/or Te) such as CuInGaSe, CuInSe2, other group III-V semiconductorsand other group II-VI compounds); and/or an alloy substrate. Thematerial contained in the substrate may be metal, semiconductor, and/orinsulator (e.g. glass, Polyethylene terephthalate (PET), sapphire, andquartz). Further, the substrate may be a thin film substrate containingmultiple layers (e.g. SOI). If the substrate comprises multiple layers,at least one of the layers may be a semiconducting film or a metallicfilm, whereas another one of the films may be an insulator. Thesemiconducting or metallic film may be disposed on a single insulatingfilm or, alternatively, interposed between a plurality of insulatingfilms. Conversely, the insulating film may be disposed on a singlesemiconducting or metallic film or, alternatively, interposed betweenmultiple semiconducting or metallic films or both.

Phase Transformation

The most rapid mechanism for crystallization of thin amorphous layers issolid phase epitaxial re-growth (SPER). In SPER, amorphous Si maytransform to crystalline Si by extending an underlying, pre-existing,extensive crystal layer. This scenario is commonly encountered duringannealing of a surface layer of a crystalline Si wafer after it has beenamorphized by ion implantation. The present disclosure relate toprocessing an amorphous substrate in which an extensive pre-existinglattice does not exist and which phase transformation occur via crystalnucleation prior to the growth of the crystals. Referring to FIG. 1,there is shown a block diagram of various mechanisms through which amaterial without extensive pre-existing lattice may transform from anamorphous phase into a crystalline phase. As known in the art, thecrystalline phase may be categorized as a poly-crystalline phase or amono-crystalline phase. The poly-crystalline phase may sometimes befurther subdivided into different categories (such as multi-, micro-,nano-crystalline etc) depending on the crystal size. However, such adistinction may not be important in the context of this disclosure, andmay not be necessary to describe FIG. 1. Accordingly, these phases maybe referred herein collectively as a crystalline phase.

As illustrated in FIG. 1, the phase transformation from the amorphousphase to a crystalline phase may occur via various mechanisms. Forexample, the transformation may occur via melting and solidificationmechanism 100 a and solid phase crystallization (SPC) transformationmechanism 100 b. In the melting and solidification mechanism 100 a andSPC mechanism, the transformation may occur via nucleation ofcrystallites and growth of the crystallites. In the SPER mechanism, thetransformation may occur by growth on the extensive pre-existing crystallattice.

In the melting and solidification mechanism 100 a, energy in the form ofradiation, heat, or kinetic energy, may be introduced to a portion ofthe amorphous substrate and melt the portion. If the condition of themolten region is adequate to induce nucleation (e.g. supercooling),crystals may nucleate as described by the classical nucleation theory.The crystals may nucleate via two schemes. The crystals may nucleateheterogeneously on pre-existing seeds. The pre-existing seeds may begrain boundaries of pre-existing crystals that did not melt uponintroduction of the energy. The pre-exiting seeds may also be theboundary between the molten region and adjacent solid region. If thepre-existing seeds are absent, the crystals may nucleate homogeneously.Upon nucleation, the crystals may grow until the growth is halted.

In the solid phase transformation mechanism 100 b, the phasetransformation may occur despite the absence of the melting. Forexample, crystals may nucleate in the region introduced with energy, andthe nucleation may be followed by the growth of the nucleated crystals.As in the case of the melt process, nucleation during SPC can occurheterogeneously if pre-existing seeds exist, or homogeneously if suchseeds are absent.

Particle Assisted Processes

In the present disclosure, particles may be introduced to a substrate toinduce the phase transformation. The phase transformation may be thatfrom the amorphous phase to one of the polycrystalline and/ormono-crystalline phases. In addition, the phase transformation may occurvia nucleation and growth of the crystals. To induce the transformation,the particles may be introduced near the upper surface of the substrate,the lower surface of the substrate, or a region between the upper andlower surfaces, or a combination thereof. If the substrate comprises twoor more different materials, the particles may be introduced to a regionnear the interface of the different materials.

Particle Species

Numerous types of particles may be introduced to induce the phasetransformation. For example, the particles that are chemically and/orelectrically inert with respect to the substrate may be used. However,chemically and/or electrically active material may also be used. Asnoted above, the particles may be charged or neutral sub-atomicparticles, atomic particles, or molecular particles, or a combinationthereof. In some embodiments, molecular particles are preferred. Inother embodiments, cluster particles are preferred. Molecular andcluster particles may be preferred as they may be introduced to thesubstrate at much higher dose and energy. In particular, molecular andcluster particles introduced to a substrate may disintegrate on impact,and the kinetic energy of the particles may be shared in the ratio ofthe atomic masses of the particle atoms. The overlapping collisioncascades may achieve result similar to introduction of atomic particlesat much higher dose rate. Due to their greater mass, the molecularparticles may also be introduced to the substrate at much higher energy.The generation of atomic and molecular species in implanters, PLAD andPIII will be familiar to those skilled in the art. A detaileddescription of the generation of cluster particles may be found in U.S.Pat. No. 5,459,326, which is incorporated in entirety by reference.

The choice of the particles introduced to the substrate may also dependon the effect of the particles on the substrate. Some characteristicsand illustrative examples are shown in Table 1.

TABLE 1 Some possible choices of ion species Characteristic Examplespecies Electrically Ge, Si, C, F, N H, He, Sn, Pb, inactive inhydrocarbon molecules, molecules silicon containing C and two or moreother elements, hydrides of silicon such as tetra-silane, moleculescontaining Si and two or more other elements Dopants B, P, As, Sb, In,Ga, Sb, Bi, Shallow Junction C, F Co-implant species Amorphizing NobleGases (including He, Xe), Ge, Si Strain producing Ge, C Bandgap Yb, Ti,Hf, Zr, Pd, Pt, Al engineering Passivating H, D Defect Pinning NCrystallization Ni, metals catalysts

Depth and Energy

When the particles are introduced to the substrate, the kinetic energyof the particles may be transferred to the substrate. The magnitude ofthe transferred kinetic energy may depend on the size, mass, and energyof the particles. For example, heavy ions introduced to a substrate mayexperience more nuclear stopping than lighter ions. When the particleslose their kinetic energy via the nuclear stopping mechanism, themechanism tends to form defects such as, for example, dangling bonds,vacancies, and di-vacancies, whose presence may enhance thecrystallization process. At the same time, kinetic energy transferred tothe substrate via electronic stopping may cause crystallization.

Depending on the energy of the particles, the location of the particlesdelivery, and the properties of the substrate (e.g. thermalconductivity, heat capacity and melting temperature of the substrate),nucleation of crystals may be initiated at the upper surface of thesubstrate; the lower surface of the substrate; the region between theupper and lower surfaces; or near the interface of different materials.Thereafter, the phase transformation may continue in a direction awayfrom the location where the transformation is initiated.

Unlike the radiation based phase transformation, energy deposited to thesubstrate via the particle introduction may peak at the surface or,alternatively, below the surface. In addition, the particles may beintroduced to the substrate at a constant energy. Alternatively, theparticles may be introduced at varied energies. For example, the energyof the particles introduced to the substrate may change while theparticles are being introduced. The change in the energy may occurcontinuously or in a sequence. If a beam-line particle system is used,the particle energy may be changed during the particle introductionusing acceleration or deceleration voltage associated with beam-linesystems described herein. If PLAD, PIII, or other plasma based system isused, the energy may be changed during the introduction by varying thevoltage applied to the substrate.

Referring to FIG. 2, there is a graph showing depth and energy ofparticles introduced to a substrate, according to one embodiment of thepresent disclosure. In the present embodiment, Ar ions are implantedinto Si thin film. As shown in FIG. 2, the points joined by the linerepresent the average range of the Ar ions and the vertical error barsrepresent the straggle in depth. The total range of all ions can then beestimated by the sum of the average range plus a multiple (one or more)of the straggle. If the Ar ions were required to be contained within asurface layer of Si of known depth, the maximum energy may be estimatedfrom this curve. The inset chart is a larger representation of the lowenergy scale of the main chart.

Spatial and Temporal Profile

In addition to the energy, the spatial and temporal profile of theparticles may be controlled. For example, the particles may beintroduced as a particle beam, and the beam may have constant or variedbeam current density (i.e. number of particles in a predetermined areafor a predetermined time). The current density may be adjusted bychanging the particle current and/or beam size; the beam dwell time bycontrolling the beam and/or substrate scanning speeds and/or pulselength; and the beam duty cycle (e.g. time between beam pulses or returntime if the beam and/or substrate are scanned).

In the present disclosure, the particles may be introduced to thesubstrate continuously or periodically in sequence. If the particles areintroduced as a particle beam, the beam may have various shapes. Forexample, the particles may be introduced as a ribbon beam or a spotbeam. The ribbon beam may have a ribbon shape or a shape where thedimension of the beam along one direction is larger than along anotherdirection. Such a ribbon beam may be wider than the substrate or,alternatively, narrower than the substrate. The spot beam, meanwhile,may have a dimension smaller than the substrate. If used, the spot beammay be scanned, either magnetically or electrostatically at a rate ofapproximately 100-1000 Hz, to resemble the ribbon beam.

If the cross section of the beam, whether a ribbon beam or a spot beam,is smaller and does not cover the entire surface area of the substrate,the beam may be additionally scanned relative to the substrate. Forexample, the beam may be scanned along 2 directions, along the widthdirection and length direction, such that the particles may beintroduced to the entire surface of the substrate. In the presentdisclosure, such scanning may be achieved by translating the substratealong the length and width directions relative to a stationary beam orby translating the beam along the length and width directions relativeto the stationary substrate. By controlling the rate of the relativescanning of the beam and/or the substrate, the phase transformation ofthe substrate may be controlled.

In addition, the particle beam introduced to the substrate may be afocused beam or a non-focused beam. In addition, the particles beam maybe uniform or non-uniform along its cross section. For example, a ribbonbeam may have a higher current density at its leading edge followed by atrailing edge having a lower current density, or vice versa. Thenon-uniform beam may have other intensity profiles. It is believed thata non-uniform beam may enhance the nucleation process and the growthprocess. For example, the non-uniform beam may have an intense leadingedge to initiate nucleation, followed by a less intense trailing edge.For example, the high density portion of the beam may initiate the phasetransformation by melting the substrate, and the low density portion ofthe beam may enhance the extent of the transformation by controlling thesolidification of the molten region.

Further, more than one beam may be operated and introduced to thesubstrate either simultaneously or sequentially. If more than one beamis used the beam may be introduced to the entire width and/or length ofthe substrate at one time.

Direction

The particle assisted phase transformation may have some advantage inorienting the crystal growth and/or crystal shapes. In the presentdisclosure, the particles may be introduced to the substrate at variousangles. Introduction of the particles at various angles may be achievedby the tilting the substrate relative to the beam and/or the beam may betilted relative to the substrate.

In one embodiment, the particles may be introduced to the substrate at0° (i.e. perpendicular to the surface of the substrate). The particlesintroduced at 0° may preferentially destroy {200} grain boundaries thatmay limit electrical conductivity in FPDs. Alternatively, the particlesmay be introduced at other angle, for example, 7°.

Substrate Condition

In addition to the parameters of the particles, the conditions of thesubstrate may be adjusted before, during, or after introduction of theparticles. For example, the temperature of the substrate may beadjusted. In one embodiment, the substrate may be heated to, forexample, approximately 500° C. prior to or during the introduction ofthe particles. Heating the substrate may mitigate thermal shock causedby the particle beam. In addition, heating the substrate may induceformation of larger crystals. For example, heating the substrate maycause the region introduced with the particles to cool at a slower rate(as this region may largely loose its energy through conduction into thesubstrate).

The crystallization may be enhanced if the substrate were cooled belowroom temperature. For example, the substrate may be cooled to atemperature ranging from about 0° C. to about −100° C. In addition,cooling the substrate may prevent the structure of the insulating filmfrom being unstable.

When the particles are introduced to the substrate, the substrate may bein vacuum or at atmospheric pressure. The vacuum pressure may be higherthan those usually associated with ion implantation (i.e. pressurehigher than 10-4 mbar) to reduce pump cost.

Exemplary Systems

Referring to FIG. 3, there is shown a block diagram of an exemplarysystem 300 for processing a substrate according to one embodiment of thepresent disclosure. The system 300 may be a beam-line particle system300. The system 300 may comprise an ion source 302; an extraction system304; an acceleration system 306; optional beam manipulation components308; and a neutralization system 310. In addition, the system 300 maycomprise an end station 312 communicating with the neutralization system310. The end station 312 may comprise a window 314 and one or moreloadlocks 316 and 318. Within the end station 312, a platen thatsupports a substrate 322 may be positioned. In addition, one or more ofsubstrate translation, cooling and/or heating sub-system 324 may bedisposed in the end station 312.

In the present disclosure, the ion source 302 may be a Bernas type, withindirectly heated cathode. Those of ordinary skill in the art willrecognize that the ion source 302 may also be other types of ion source.Meanwhile, the extraction system 304 may be a single slit or,alternatively, a multiple slit extraction system 304. The extractionsystem 304 may be translatable in one or more orthogonal directions. Inaddition, the extraction system 304 may be designed to extract atemporally constant beam current. In addition, the extraction system 304may extract the particle continuously or intermittently. The extractionsystem 304 may also focus the particle beam or beamlets to allow adesirable spatial and/or temporal beam profiles. The particles beamextracted via the extraction system 304 may have energy of approximately80 keV.

If higher energy is required, the system 300 may include an accelerationsystem 306 that may accelerate the particle beam. The system 300 mayalso include one or more additional, optional beam manipulationcomponents 308 to filter, scan, and shape the particles to a particlebeam. As illustrated in FIG. 4, a specific example of the system 300,the optional beam manipulation components 308 may include a first magnetanalyzer 406, a first deceleration (D1) stage 408, a second magnetanalyzer 410, and a second deceleration and a second deceleration (D2)stage 412. In the present disclosure, the first magnet analyzer 406, asubstantially dipole magnet, may filter the particles based on theparticles' mass and energy such that particles of undesired mass and/orenergy will not pass through the magnet analyzer 406. Meanwhile, thesecond magnet analyzer 410, another substantially dipole magnet, may beconfigured to collimate the particles into a particle beam havingdesired shape (e.g. ribbon) and/or dimension. D1 and D2 decelerationstages 410 and 412 may manipulate the energy of the particles passingthrough such that the particles may be introduced to the substrate at adesired energy. In one embodiment, the D1 and/or D2 may be segmentedlenses capable of minimizing the space charge effect and maintainingspatial integrity of the beam.

Although not shown, the beam manipulation components may also includeone or more substantially quadrupole magnets or einzel lenses to focusthe beam. Further, the beam manipulation components may also includemagnetic multipoles or rods such as described in U.S. Pat. Nos.6,933,507 and 5,350,926 to control the uniformity of the beam profile.

Returning to FIG. 3, the charge neutralization system 310, according tothe present embodiment, may also be included to reduce charge build-upin the substrate 322. The charge neutralization system 310 may be one ormore systems of hot filament, or microwave, or rf driven type, such asthat described in U.S. patent application Ser. No. 11/376850.Alternatively, the charge neutralization system 310 may be an electronsource.

In the end station, the environment around the substrate may becontrolled in order to prevent, for example, deposition of othermaterials on the substrate or to promote passivation to enhance thecrystallization process. To control the environment, the end station 312may include a thin foil window or a differentially pumped aperture 314,through which the particles may enter, and one or more loadlocks 316 and318, through which the substrate may be admitted. The loadlocks 316 and318 may be replaced by one or more differentially pumped stages throughwhich the substrate may be admitted.

The end station 312 may also contain substrate movement, cooling, andheating subsystem 324. Examples of sub-system 324 may include a chiller,a heat source, a roplat capable of translating/rotating the substratealong several axes. Specific examples of the chiller may be found inU.S. patent application Ser. No. 11/504,367, 11/525,878, and 11/733,445,each of which is incorporated by reference in entirety. Specificexamples of the heat source may be a laser, flash lamp, platen providingfluid heating, resistive heat source, or those described in U.S. patentapplication Ser. Nos. 11/770,220 and 11/778,335, each of which isincorporated by reference in entirety.

To monitor the process and substrate parameters/conditions, one or moreparameters/conditions measuring components may also be included near thesubstrate 322. Such components may be coupled to one or morecontrollers, and the controllers may control the parameters/conditionsof the substrate and/or the particles based upon the signals from themeasuring components.

Referring to FIG. 5, there is shown another exemplary system forprocessing a substrate according to another embodiment of the presentdisclosure. In particular, the system 500 may be a PLAD, PIII system, orother plasma based substrate processing system. PLAD system 500 maycomprise a chamber 501 including top section 502 and a lower section504. The top section 502 may include a first dielectric section 506 thatextends in a generally horizontal direction and a second dielectricsection 508 that extends in a generally vertical direction. In oneembodiment, each dielectric section 506 and 508 may be ceramic that ischemically resistant and that has good thermal properties. The topsection 502 may also include at least one or more antennas 510 and 512.The one or more antennas 510 and 512 may be, for example, a horizontalantenna 510 and/or a vertical antenna 512. In one embodiment, thehorizontal antenna 510 may be a planar coil having multiple windings,whereas the vertical antenna 512 may be a helical coil of multiplewindings. At least one of the antennas 510 and 512 may be electricallycoupled to a power supply 514 via an impedance matching network 516.

On the lower section 504 of the system 500, a platen 520 and a substrate522 supported by the platen 520 may be positioned at a predeterminedheight below the top section 502. However, it is also contemplated thatthe platen 502 ad the substrate 522 may be positioned in the top section502. A bias voltage power supply 524 may be electrically coupled to theplaten 520 to DC or RF bias the platen 520.

In operation, at least one of the antennas 510 and 512 may be RF or DCpowered by the power source 514. If only one of the antennas 510 and 512is RF or DC powered, the other one of the antennas 510 and 512 may be aparasitic antenna. The other one of the antennas 510 and 512 may be aparasitic antenna as it is not electrically coupled to the power source514. Instead, the other one of the antennas 510 and 512 is magneticallycoupled to the antenna that is powered by the power source 514.Alternatively, both of the antennas 510 and 512 may be powered by thepower source 514 with an RF current. Thereafter, at least one of theantennas 510 and 512 induces the RF currents into the system 500 via thefirst and second dielectric sections 506 and 508. The electromagneticfields induced by the RF currents may covert the gas contained in thesystem 500 into plasma. Meanwhile, the bias voltage power supply 524 maybias the platen 520 to attract the charged particles in the plasma tothe substrate 522. Additional details of the system 500 may be found inU.S. patent application Ser. No. 11/766984; application publication No.2005/0205211; application publication No. 2005/0205212, and applicationpublication No. 2007/0170867, each of which is incorporated in entiretyby reference.

Optional Components

In addition to the components described above, the exemplary systems300-500 may optionally include one or more masks between the particlesource (e.g. ion source or plasma) and the substrate. If included, themask may preferentially be a carbon (C) based material, Si basedmaterial (e.g. SiC), or refractory metal, such as W or Ta, containingmaterial. However, other materials may also be used. Such a mask mayhave one or more aperture having various shapes including chevron shapeto control the shape of the beam incident on the substrate.

FPD

Hereinafter, description of several applications of the particle inducedphase transformation is provided. As noted above, the particles may beintroduced into a Si layer of a thin film substrate to induce the phasetransformation from the amorphous to the crystalline phase. For purposeof clarity, a comparison of the particle induced phase transformation ismade with the ELA process.

In the present embodiment, the particles may be directed to an FPDhaving an amorphous Si film of about 500 Å thick disposed on aninsulating film. The insulating film may be, for example, amorphousglass or Corning 1737 glass having a thickness of about 0.7 mm, quartz,plastic, or sapphire. However, those of ordinary skill in the art willrecognize that other types of insulating film may also be used.

In ELA process, a single laser pulse may deliver an energy pulse of 360mJ/cm² in a 12 nanosecond long pulse. This equates to a power density of3×10¹⁰ W/m². If an Ar ion beam is directed to the Si film, the beam mayhave an energy of 20 keV. With such energy, all of the directed Ar ionsmay not penetrate the substrate beyond the Si layer (see FIG. 2). If aribbon shaped Ar particle beam is used, the beam may be assumed to havedimensions of 300 mm wide by 0.1 mm tall. With a beam current of 25 mA,this implies a power density of 1.7×10⁷ W/m².

In ELA process, the laser beam incident on the substrate may heat the Silayer to 1000° C., near the melting temperature of amorphous Si. Uponincidence, the laser beam may initiate at least a partial melting of Silayer. The thermal diffusivity for Si is relatively high, varyingbetween ˜1 cm²/sec at room temperature and 0.1 cm²/sec at 1400K. Hence,even if the laser energy is absorbed in the top few nm of the Sisurface, absent any latent heat effects, there may be a very smalltemperature gradient within the Si layer. Heat may diffuse from the Siinto the glass. The diffusivity for the glass is small (˜0.005 cm2/sover a large temperature range), and so a large thermal gradient mayexist across the thick glass layer. The results of the model shown inFIG. 6, calculate that the glass even within 0.1 μm of the Si, does notreach above 500° C.

As the particle beam has a lower power density, the exposure time neededto deposit sufficient energy to heat the Si film may be higher (80 ms)compared to the laser (12 ns). In addition, as the heat deposited to thesubstrate via the particles may be lost to the insulating via thermalconduction, more energy may be needed to heat the Si film sufficiently.Under these assumptions, the insulating film within 50 μm of the Si maybe heated above 600° C. Nevertheless, sufficient amount of theinsulating may not be heated above its glass transition (or melting)temperature such that these conditions may be acceptable.

If the height of the ribbon beam were to increase to 1 mm, it may takeapproximately 2.4 seconds to sufficiently heat the Si film, in whichtime the peak temperature of the bottom of glass may reach 600° C. Thisexample, compared to the 0.1 mm case in FIG. 7, demonstrates the need tokeep the power density of the beam as high as possible. This may beachieved by maintaining the beam area as small as possible, increasingbeam current, and/or increasing the beam energy. The mass of the ionspecies may also be increased. The use of a molecular particle beam maybe desirable as it allows the use of higher beam energies. At the sametime, the higher beam energy may reduce additional detrimental effectssuch as space charge blow-up that may otherwise limit the beam currentsand the beam focusing.

The particle beam irradiation may retain the solid Si in the amorphousphase, allowing melting to occur at 1300K. Crystalline Si does not meltuntil 1683K. Therefore if the amorphous Si undergoes crystallizationbefore melting commences, more power may be required to completely meltthe material. Also, liquid Si may reflect a portion of the laserradiation and so coupling power into the bulk of the Si may be difficultonce the Si surface has melted. The presence of a particle beam duringthe cooling and crystallization phase may influence the production ofhigh quality material.

Thin Film Solar Cell

The particle induced phase transformation described in the presentdisclosure may also be applied to manufacture of thin film solar cells.As known in the art, amorphous Si is a direct band gap material and mayabsorb light more efficiently than crystalline Si, an indirect band gapmaterial. In addition, amorphous Si absorbs more light in the visiblespectrum than crystalline Si. However, amorphous Si has lower electricalconductivity. As such, amorphous Si may preferably transform incidentradiation to electrical current, whereas crystalline Si may preferablytransfer the generated electrical current. Accordingly, the solar cell,according to the present embodiment, may preferably have a layer ofamorphous Si above another layer of crystalline Si. Incident radiationat visible wavelengths may be efficiently converted into photocurrent inthe amorphous Si. Light not converted in the amorphous layer (includinginfra-red radiation) may be converted into photocurrent in thecrystalline Si.

Referring to FIG. 8, there is shown a process that may be incorporatedin preparing a substrate according to another embodiment of the presentdisclosure. In the present embodiment, the substrate may be a thin filmsolar cell with crystalline and amorphous layers. In another embodiment,the substrate may be a semiconducting layer of a FPD that is disposed onan insulating layer (not shown). As illustrated in FIG. 8A, an amorphousSi layer 802 may be deposited onto a glass layer (not shown). The Silayer 802 may have thickness of 1.5 μm, whereas the glass layer may havethickness of 3 mm. The particles 804 having a predetermined dose andenergy may then be introduced to the amorphous Si layer 802. Asillustrated in FIG. 8B, the particles 804 may be introduced below thesurface of Si layer to crystallize a lower portion of Si layer 802,without inducing crystallization of the upper portion of amorphous Silayer 802. The resulting substrate may be used in a solar cell having anamorphous Si layer 802 disposed on the crystal Si layer 806.

Referring to FIG. 9, there is shown a process that may be incorporatedin preparing a substrate according to another embodiment of the presentdisclosure. In the present embodiment, the substrate may be a thin filmsolar cell with crystalline and amorphous layers. In another embodiment,the substrate may be a semiconducting layer of a FPD that is disposed onan insulating layer (not shown). As illustrated in FIG. 9A, an amorphousSi layer 902 may be deposited onto a glass layer (not shown).Thereafter, particles 904 having a predetermined dose and energy may beintroduced to the amorphous Si layer 902 to crystallize the entire Silayer 906 (FIG. 9B). As illustrated in FIG. 9C, a plurality of particlesof second species 908, energy, and dose may be introduced to thesubstrate to amorphize a layer near the surface of the crystalline Silayer. The resulting solar cell may have an amorphous top Si layer 904and a crystalline lower Si layer 902.

Referring to FIG. 10, there is shown a process that may be incorporatedin preparing a substrate according to another embodiment of the presentdisclosure. In the present embodiment, the substrate may be a thin filmsolar cell with crystalline and amorphous layers. In another embodiment,the substrate may be a semiconducting layer of a FPD that is disposed onan insulating layer (not shown). As illustrated in FIG. 10A, anamorphous Si layer 1002 may be deposited onto a glass layer (not shown).Thereafter, particles 1004 having a predetermined dose and energy may beintroduced to the amorphous Si layer 1002 to crystallize a sub-layer1006 within the Si layer 1002 (FIG. 10B). Although FIG. 10B illustrate asub-layer disposed near the upper surface of the Si layer 1002, those ofordinary skill in the art should recognize that the sub-layer 1006 maybe positioned near the upper surface, near the lower surface, oranywhere between the upper surface and the lower surface of Si layer1002.

After forming the crystalline sub-layer 1006, one or more of thecrystals in the sub-layer 1006 may be grown away from the sub-layer 1006until the entire Si layer 1002 may be crystallized. The crystals may begrown via one of furnace annealing, rapid thermal annealing (RTA),flashlamp annealing, and laser annealing. Alternatively, the crystalsmay be grown by particle assisted annealing. For example, the same oranother types of particles (not shown) having another predetermined doseand/or another predetermined energy to the region below the crystallizedsub-layer to extend the grain boundary of one or more crystals towardthe lower surface of the substrate. In the process, the entire Si layer1002 may contain one or more crystals having grain boundaries thatextend in a vertical direction. The present embodiment may also includean optional amorphizing step to amorphize a portion of the newlycrystallized Si layer 1006. For example, the particles 1010 may then beintroduced to the newly crystallized Si layer 1002 to amorphize at leasta portion of the newly crystallized Si layer 1002 (FIG. 10D) to form anamorphous sub-layer 1012. In the present disclosure, the particlesintroduced to the newly crystallize Si layer 1002 the same particles asthose used to crystallize the previous amorphous Si layer 1002.Alternatively, the the particles introduced to the newly crystallize Silayer 1002 may be different from those used to crystallize the previousamorphous Si layer 1002. The above process may be used to crystallize athick amorphous Si layer.

The particle induced phase transformation may also be used tomanufacture an efficient polycrystalline Si solar cell. The grainboundaries of crystals may be efficient sites for gettering impurities,such as metal contaminants. In addition, grain boundary may serve as abarrier for charge carriers' mobility, inhibiting the carriers fromtraveling through the boundary. Accordingly, polycrystalline solar cellshaving multiple crystals, thus multiple grain boundaries, may haverelatively low electrical conductivity if the grain boundaries arelocated across the path of the charge carriers. In the polycrystallinesolar cells, electrical current generated at the upper surface must betransported to contact areas, which are generally located at the lowersurface of the solar cell. If the grain boundaries in thepolycrystalline solar cells are positioned across the path of the chargecarriers, the efficiency of the solar cells may be lowered. As such, itmay be desirable to manufacture polycrystalline solar cells having grainboundaries oriented in parallel manner relative to the path of thecharge carriers.

To manufacture an efficient polycrystalline solar cell, an amorphous Sisubstrate may be prepared. Thereafter, the upper surface of the Si layermay be crystallized, and the crystals may grow downward per solid phaseepitaxial regrowth (SPER). The ion energy may be chosen so that thepower density delivered to the substrate may be maximized. This maycorrespond to an energy of between 40 to 100 kev, where typical ion beamsystems can extract the maximum beam currents from an ion source andwhere space charge effects are reduced for beam transport and focusing.Such an ion beam may cause crystallization near the surface of thesilicon which in turn may seed SPER downwards until the whole layer iscrystallized. The SPER may take place as part of the beam inducedcrystallization step, or in a further annealing step that may use one ormore of furnace, RTA, flashlamp, laser or other annealing methods. Theresulting substrate will likely to have crystals with verticallyextending grain boundaries. Thereafter, particles of second species,energy, and dose may be introduced to the substrate to amorphize a layernear the surface of the polycrystalline substrate. The solar cell maythen have a structure of amorphous Si layer above vertically extendingpolycrystalline Si layer. As noted above, such a solar cell will likelyto convert radiation energy to electrical energy more efficiently, and,at the same time, transport the converted electrical energy moreefficiently.

In the present disclosure, the size and orientation of the boundariesmay be influenced by the choice of the particle beam conditions used toassist the crystallization of the top layer. Phosphorous may be afavorable species as it is a good getter species, and may be the dopantof choice for the solar cell. The direction of implant may be chosen toinfluence the grain orientation. The whole active layer may beimplanted, or the surface layer may be implanted to create a topcrystalline surface with few voids, and the rest of the substrate may beregrown by SPER.

The terms and expressions which have been employed herein are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding any equivalentsof the features shown and described (or portions thereof), and it isrecognized that various modifications are possible within the scope ofthe claims. Other modifications, variations, and alternatives are alsopossible. Accordingly, the foregoing description is by way of exampleonly and is not intended as limiting. What is claimed is any featuredetailed herein.

1. A method for processing a substrate in an amorphous phase, the method comprising: disposing a substrate having an upper surface and a lower surface on a platen contained in a chamber; generating a plasma containing a plurality of charged particles above the upper surface of the substrate, the plasma having a cross sectional area equal to or greater than a surface area of the upper surface of the substrate; applying a first bias voltage to the substrate to attract the charged particles toward the upper surface of the substrate; introducing the charged particles to a region extending under entire upper surface of the substrate; and initiating, concurrently, a first phase transformation in the region from the amorphous phase to a crystalline phase.
 2. The method of claim 1, wherein the charged particles are introduced to the region at a rate of approximately 5×10¹⁴ particles/cm² sec or greater.
 3. The method of claim 1, further comprising: adjusting the bias applied to the substrate whilst the introducing of the particles to the first region.
 4. The method of claim 3, wherein the adjusting comprises increasing the bias.
 5. The method of claim 1, further comprising: adjusting temperature of the substrate prior to introducing the particles to the region.
 6. The method of claim 5, wherein the adjusting the temperature comprises decreasing the temperature.
 7. The method of claim 1, wherein the charged particles comprises one or more species selected from a group consisting of: He, Ne, Ar, Kr, Xe, and Rn.
 8. The method of claim 1, wherein the charged particles comprises molecular ions.
 9. The method of claim 1, wherein the charged particles comprises Ga ions.
 10. The method of claim 1, wherein the region comprises Si and wherein the charged particles comprises one or more species selected from a group consisting of C and Ge ions, so as to convert the region to a stressed region.
 11. The method of claim 1, wherein the region comprises a material selected from Group IV elements and wherein the charged particles comprises one or more species chosen from a group consisting of B, Ga, In, P, As, Sb, and Bi, so as to change an electrical property of the region.
 12. The method of claim 1, wherein the region comprises a material selected from Group IV elements and wherein the charged particles comprises one or more species chosen from a group consisting of Yb, Ti, Zr, Hf, Pd, Pt, and Al, so as to change a bandgap property of the region.
 13. The method of claim 1, wherein the region comprises a material selected from Group IV elements and the charged particles comprises one or more species chosen from a group consisting of C containing ions, Si containing ions, Ge containing ions, F containing ions, N containing ions, H containing ions, He containing ions, Sn containing ions, and Pb containing ions, so as to prevent changing of an electrical property of the region.
 14. The method of claim 1, wherein the region comprises a material selected from Group IV elements and the charged particles comprises metallic ions so as to increase a rate of the transformation of the region from the amorphous phase to the crystalline phase.
 15. The method of claim 15, the metallic ions comprises Ni ions.
 16. The method of claim 1, further comprising: transforming phase of entire region from the amorphous phase to the crystalline phase, the region being less than entire substrate.
 17. The method of claim 17, wherein the region comprises at least one crystal.
 18. The method of claim 18, further comprising: extending a boundary of the at least one crystal beyond the region of the substrate until a phase of the entire substrate is transformed to the crystalline phase. 